1. Field of the Invention
This invention deals with the art of hydrophilizing a porous hydrophobic membrane.
2. Prior Art
In recent years, hydrophobic membranes made of polyethylene, polypropylene, polytetrafluoroethylene or the like have now been used in an artificial kidney, plasmapheresis and various kinds of water treatments since they have excellent chemical resistance and microbial resistance.
Although these hydrophobic membranes are porous, water and blood plasma, if not subjected to a high pressure, are not allowed to pass through or permeate them. Therefore, such hydrophobic membranes under consideration need to be hydrophilized to allow water and blood plasma to permeate it.
One method of hydrophilizing such a porous hydrophobic membrane has been to first pass a liquid such as alcohol through the pores of the membrane and then to replace this liquid by water. With this method, so long as the water is present in the pores of the hydrophobic membrane, the water is allowed to pass through the pores of the membrane either freely or under a small pressure, depending on the size of the pores of the hydrophobic membrane. However, once the water is removed from the pores of the hydrophobic membrane so that the pores become dry either partially or entirely and are filled with air, the hydrophilized hydrophobic membrane is rendered hydrophobic again, and the water is not allowed to pass through the pores of the membrane if it is not subjected to a high pressure. Thus, when the hydrophobic membrane is hydrophilized with this conventional method, it must be always kept in contact with water to maintain a hydrophilic nature. This is not desirable from the viewpoint of practical use.
When a porous hydrophobic membrane of the type described above is used for the treatment of blood, it is necessary that the membrane should be subjected to sterilization. In the case of ethylene oxide gas sterilization, the membrane has to be hydrophilized while it is maintained in a sterilized state. This procedure is cumbersome. Also, in the case of formalin sterilization using an aqueous solution of formalin, a blood treatment device incorporating a hydrophobic membrane unit must be washed to remove the residual formalin solution before the blood treatment is carried out. In this case, once the formalin solution is discharged from the blood treatment device to effect a subsequent washing, the air is introduced into the pores of the hydrophobic membrane to lower the liquid permeability for the reasons mentioned above. Therefore, it is necessary that the formalin solution in the blood treatment device should be replaced by a washing water in such a manner that the air will not be introduced into the pores of the hydrophobic membranes. This procedure is also troublesome and requires much time and labor.